2 POINT MUTATIONS IN THE HORMONE-BINDING DOMAIN OF THE MOUSE GLUCOCORTICOID RECEPTOR THAT DRAMATICALLY REDUCE ITS FUNCTION

Mouse lymphoma cell line W7M320b, a mutant WEH17 line, requires higher than normal concentrations of glucocorticoid to elicit the hormone responses that are characteristic of this lineage. Complementary DNA clones representing the glucocorticoid receptor (GR) mRNA were derived from the mutant cells, and the sequences coding for the hormone-binding domain were substituted for the analogous wild-type sequences in a GR cDNA expression vector. The function of the resulting GR proteins was tested by transient expression in COS-7 cells along with a glucocorticoid-inducible reporter gene in the presence of varying concentrations of glucocorticoid. From these assays and DNA sequence analyses, two independent functionally significant point mutations in the GR hormone-binding domain were identified. A mutant GR protein containing the single amino acid substitution, Pro547 to Ala, was still functional as a transcriptional activator, but only at hormone concentrations 100 times higher than those required by the wild-type receptor. A second mutant GR protein with a Cys742 to Gly substitution was unstable and almost completely nonfunctional.